You will get better results if you fit a small propeller with a shaft
bearing 3 or 4 inclined blades (diameter around 4-6 cm) to a simple power
drill fixed on a benchtop stand. Smaller benchtop laboratory mixers are
also suitable (e.g. IKA Eurostar, etc.) for small amounts. Various blade
shapes and angles are possible, with or without guard rings, like those
available as paint mixers. They can be operated at around 2000 rpm (or even
3000 rpm for some drill / variator combinations).
The more sophisticated models have an electromagnetic brake to better
control short mixing times for reactive products (e.g. Ytron, not described
on their website).
On Thu, 2006-02-23 at 14:30 +0100, infinitum wrote:
Now admittedly I am not a mixer expert, but high rpms with mixing a high
viscosity liquid doesn't sound right to me. I guess right around the
propeller it would get mixed, but as there will be little flow in the
container (this in contrast with low to medium viscosity liquids, and
highly sheer thinning, such as paints).
I would go for low rpm, high sheer mixers where the mixing elements move
a larger distance and cover the complete container.
Please correct me if this intuition is wrong.
<FONT COLOR="#000000">> Hi,</FONT>
<FONT COLOR="#000000">> I currently use an IKA high shear homogenizer for
mixing PU foam</FONT>
<FONT COLOR="#000000">> components but I find that it is not very efficient
due to the high</FONT>
<FONT COLOR="#000000">> viscosity of the prepolymer and polyols. I would be
interested to know</FONT>
<FONT COLOR="#000000">> how others mix their PU components.</FONT>
<FONT COLOR="#000000">> Kind regards,</FONT>
<FONT COLOR="#000000">> Gillian</FONT>
It is often possible to mix foam ingredients in a cup with a spatula (low
shear, low rpm) and to get decent quality. Industrial foaming machines (low
pressure types) on the other hand, work with high shear/high rpm rotors in a
small mixing chamber where all the ingredients are pumped through at a set
rate. If you slow down the rotor, you quickly get poor foam.
The set-up I proposed is a practical method widely used in laboratories for
mixing batchwise, small amounts (up to about 500 g) raw materials up to
about 100 Pa.s at room temperature. Maybe I could have added that it helps
to move the cup around the mixer while it's on to optimise homogeneity. Foam
ingredients are reactive and mixing should be completed before creaming,
which may take place within 5-10 seconds. Also traditional high shear mixers
with rotor/stator are more difficult to clean.
Check out centrifugal mixers- you won't believe how amazing and fast
they are for batch mixing high viscosity materials (not good for
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